netdev - Re: [PATCH net-next] bridge: remove a redundant synchronize

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Date:	Thu, 04 Apr 2013 08:44:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	David Miller <davem@...emloft.net>, vfalico@...hat.com,
	netdev@...r.kernel.org, stephen@...workplumber.org
Subject: Re: [PATCH net-next] bridge: remove a redundant synchronize_net()

On Thu, 2013-04-04 at 17:35 +0200, Jiri Pirko wrote:

> It can be converted now to call_rcu. synchronize_rcu is making sure
> no packet is in flight when changing modes.

What changes exactly ? You don't really answer to my question with this
very vague sentence.

Because maybe the synchronize_net() in netdev_rx_handler_unregister()
is enough and you dont even need the call_rcu(). Thats was my question.

RCU barriers are not magical things we add when we are not exactly sure
of what is happening.

Like other barriers (wmb(), smb_wmb(), ...) we should document or
understand why they are needed.

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